1. Field of the Invention
The present invention relates to an imaging apparatus, an imaging method, a recording medium, and a program. Particularly, the present invention relates to an imaging apparatus, an imaging method, a recording medium, and a program capable of reducing flicker that occurs during imaging performed by a video camera using an XY-address-scanning imaging device under a fluorescent-lighted environment.
2. Description of the Related Art
As is conventionally known, flicker occurs due to fluorescent light during imaging of moving images performed by a video camera under a fluorescent-lighted environment.
More specifically, when images of a subject are taken by a video camera under a fluorescent-lighted environment that is directly generated by a commercial AC power supply, a difference between a frequency of a change in luminance (light intensity) of fluorescent light (twice the frequency of the commercial AC power supply) and a vertical synchronization frequency of the camera causes a temporal change in contrast in output video signals, that is, so-called flicker (fluorescent flicker).
For example, assume that images of a subject are taken by a CCD (charge-coupled device) camera of an NTSC (National Television System Committee) method (the vertical synchronization frequency is 60 Hz) under non-inverter fluorescent light in an area using a commercial AC power supply frequency of 50 Hz. In that case, one field period is 1/60 seconds, whereas a period of change in luminance of the fluorescent light is 1/100 seconds. Accordingly, exposure timing is different in each field with respect to a change in luminance of the fluorescent light, so that the amount of exposure of each pixel changes in each field.
Under these circumstances, flicker-combating imaging apparatuses have been proposed.
For example, a video camera preventing occurrence of flicker by using exposure time has been proposed. Also, regarding a video camera using an XY-address-scanning imaging device, a technique of correcting occurrence of flicker by using a prepared pattern of change in luminance and hue has been proposed. Also, a technique of reducing an effect of flicker by using frames having a phase difference of 180 degrees has been proposed.
Also, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2004-222228 discloses the following technique. That is, an input image signal is integrated over time of one horizontal period or more, a differential value of integration values in adjacent fields is normalized by an average of integration values in three sequential fields, discrete Fourier transform is performed on the normalized differential value so that a spectrum is extracted, a flicker coefficient is estimated on the basis of the extracted spectrum, whereby an effect of flicker in the input image signal is reduced.